Epoxy resins are a well established class of curable (thermosettable) compositions which find utility in a myriad of applications. The curing of epoxy resins is effected by a wide range of curing agents, for example, the primary and secondary polyamines including the aliphatic amines, cycloaliphatic amines and aromatic amines; dicarboxylic acids and anhydrides thereof; aromatic hydroxyl containing compounds; imidazoles; guanidines; urea-aldehyde resins, melamine-aldehyde resins and alkoxylated derivatives thereof; amidoamines and various combinations thereof. In many of the applications served by epoxy resins, it would be desirable to improve one or more of the physical and/or mechanical and/or thermal properties of the cured products.
The present invention provides diamino-alphaalkylstilbene compositions which are useful for curing epoxy resins. Certain of these compositions, notably the 4,4'-diamino-alpha-alkylstilbenes and the N,N'-dialkyl-4,4'-diamino-alpha-alkylstilbenes, are mesogenic. The aforesaid mesogenic diamino-alphaalkylstilbenes, when combined with certain epoxy resins, for example, the diglycidyl ether of 4,4'-dihydroxyalpha-methylstilbene, exhibit ordering of the molecular chains in the melt phase. This morphology is susceptible to flow induced orientation during processing which can result in enhanced unidirectional mechanical properties. Rigidity imparted to the thermoset matrix by the rigid rodlike, mesogenic structure can additionally result in enhanced thermal stability. This is not possible to attain to any significant extent with conventional (non-mesogenic) diamine curing agent and epoxy resin compositions.
The term "mesogenic" as is used herein designates compounds containing one or more rigid rodlike structural units which have been found to favor the formation of liquid crystal phases in the case of low molar mass substances. Thus the mesogen or mesogenic moiety is that structure responsible for molecular ordering.